Universal Mobile Telecommunications System (UMTS) refers to a third-generation asynchronous mobile communication system that employs Wideband Code Division Multiple Access (WCDMA) on the basis of Global System for Mobile Communications (GSM) and General Packet Radio Service (GPRS) used primarily in Europe.
The 3GPP (3rd Generation Partnership Project), the UMTS standardization body, has proposed Long Term Evolution (LTE) as next generation mobile communication technology for the UMTS system. The LTE system is based on high-speed packet-based communication technology supporting a maximum data transfer rate of about 100 Mbps, and is expected to be commercially available by about 2010. To achieve this, various approaches have been considered, such as reducing the number of nodes on a communication path and reducing the number of protocol layers supporting wireless channels through simplification of the network architecture.
Particularly in LTE, when resource allocation is conducted through packet-based scheduling and communication is performed using newly allocated resources, heavy traffic may be induced by frequent transmission of control information including scheduling requests and resource allocation indications. To avoid this, semi-persistent scheduling (SPS) has been employed to allocate semi-persistent resources.
A mobile terminal (or user equipment) may reduce power consumption through discontinuous reception (DRX). When DRX operation is enabled, the receiver of the mobile terminal is turned on to receive data during a preset duration and is turned off during the remainder of the time. DRX operation is defined by DRX cycles, and each DRX cycle is composed of an on-duration during which the receiver is turned on and an off-duration during which the receiver is turned off.
However, as it is impossible to allocate semi-persistent resources during the off-duration, even if resources allocatable as semi-persistent resources are available in the off-duration, the base station may be forced to postpone semi-persistent resource allocation until the on-duration of the next DRX cycle. In a worst case scenario, when resources allocatable as semi-persistent resources are not available in the on-duration, the base station may be unable to allocate semi-persistent resources to the mobile terminal even though resources are available in the off-duration, causing service interruption.